1. Field of the Invention
The present invention relates to an eyepiece optical system which is used in combination with an objective optical system of a telescope or binoculars.
2. Description of the Related Art
In the prior art, various eyepiece optical systems which position an image formed by the objective optical system between predetermined lens groups constituting the eyepiece optical systems have been proposed. For example, Japanese Unexamined Patent Publication No. Hei-8-76033 proposes an eyepiece optical system in which the first lens group has negative power and the second lens group has positive power, and an intermediate image is formed between these two lens groups. However, since the power of the first lens group is strong, a large amount of aberrations occur, and it is difficult to correct the aberrations through the second lens group. Also, the diameter of the second lens group tends to be made larger in order to perform the correcting of aberrations.
Furthermore, Japanese Unexamined Patent Publication No. Hei-8-5937 proposes an eyepiece optical system which arranges the first lens group constituted by a meniscus lens element, an intermediate image, the positive second lens group, and the positive third lens group, in this order from the object. However, throughout the embodiments taught therein, since the first lens group has positive power, the Petzval sum of the entire lens system, including the second and third lens groups, is large. In other words, field curvature increases, and the eye relief becomes shorter.